1. Field
Embodiments of the present invention relate to a coil assembly, and more particularly to a coil assembly capable of maintaining a stable contact state with a printed circuit board and improving performance thereof by preventing electromagnetic waves.
2. Description of the Related Art
Generally, various kinds of brake systems are offered in vehicles to obtain a braking force. For example, anti-lock brake system (ABS) which prevents vehicle from skidding, electro-hydraulic braking (EHB) system, electronic stability control (ESC) system, and the like are offered and used.
Such an electronically controlled brake system is provided with a plurality of solenoid valves for controlling a brake fluid pressure transmitted to wheel brakes, a low pressure accumulator for storing oil temporarily, a pump for forced pumping the oil stored in the low pressure accumulator, a hydraulic control unit (HCU) equipped with a high pressure accumulator or the like for reducing pressure pulsation of the oil being pumped by pump, and an electronic control unit (ECU) for controlling electrically operated constituent elements.
The electronic control unit equipped with a printed circuit board (PCB) and coupled to the hydraulic control unit through a fastening member such as a bolt or the like controls constituent elements operated electrically. In addition, the solenoid valve includes a coil assembly which forms an electromagnetic field when a coil is wound and electric power is applied, and a valve assembly which opens and closes an inside flow channel by the electromagnetic field formed by the coil assembly. Here, in the coil assembly, for driving the valve assembly, lead wires of both poles formed in the coil assembly are coupled to the printed circuit board using soldering to make electrical contacts, a portion of the valve assembly is inserted into the center of the coil assembly, and the other portion is press-fitted into the hydraulic control unit made of an aluminum material.
In the meantime, in the case of electronic control unit which drives an actuator such as a motor, a solenoid coil, and the like, generally a control is achieved using a control method of pulse width modulation (PWM) drive in which a current flowing through a coil can be controlled by controlling a duty-ratio of the pulse width modulation. However, since both coils in a motor and a solenoid valve are inductive actuator, an electro-magnetic compatibility (EMC) noise is generated due to the pulse width modulation drive.
Here, for a smooth operation of the solenoid valve controlled electrically, a structure for shielding the electromagnetic waves between the electronic control unit and the hydraulic control unit is disclosed. For example, electromagnetic waves may be shielded by equipping a grounding spring between the printed circuit board and a counterpart metal component to make a contact therebetween or by making a contact between the solenoid valve and the printed circuit board through a separate coupling member.
However, for shielding such electromagnetic waves, since separate members have to be provided for making a contact structure between the printed circuit board and a body of the motor or between the printed circuit board and the hydraulic control unit, there are problems of cost increase and manufacturing difficulties in the brake system.
In addition, in the case of the lead wires coupled to the printed circuit board for operation of the solenoid valve through a soldering work, when a crack develops in the coupled portion due to using a coil heavier than a specific weight or due to an external vibration, a problem occurs where in a severe case the solenoid valve operation stops.